1. Field of the Invention
The present invention relates to a method for high-sensitive silver staining, more specifically, to an improved method for silver staining of DNA which comprises the steps of linking DNA to a polymer which has a high affinity for the DNA and binding of a plenty of silver ions to the DNA-polymer complex.
2. Description of the Prior Art
In general, silver staining is realized by carrying out selective reducing silver ions which are linked to a target material of interest by employing chemical or light (see: Beidler, J. L. et al., Anal. Biochem., 126:374(1982); Goldman. D. and Merril, C. R., Electrophoresis, 3:24(1982)) and detecting light-scattered color of the silver grains produced therefrom (see: Merril, C. R. et al., Proc. Natl. Acad. Sci., USA, 85:453(1988)).
Silver staining methods currently used are largely classified as the following: an alkaline method which reduces a diamine complex of silver nitrate formed under a strong alkaline condition by subjecting the complex in a weakly acidic solution containing formaldehyde; and, an acidic method which reduces silver nitrate in a formaldehyde solution (see: Bassam, B. J. et al., Applied Biochemistry and, Biotechnology, 42:181(1993)).
Although the silver staining technique, at the begining, was developed to detect traces of protein electrophoresed on acrylamide gel (see: Switzer, R. C. et al., Anal. Biochem., 98:231(1979)), through continuous improvement and modification, it has been universally used for detection of lipopolysaccharides (see: Tsai, C. and Frasch, C. E., Anal. Biochem., 119:115(1982)) and nucleic acids (see: Somerville, L. L. and Wang, K., Biochem. Biophys. Res. Commun., 102:54(1981), and proteins as well.
Until now, a variety of silver staining methods for the detection of DNA have been developed as the following: a diamine complex silver staining method (see: Wary, W. et al., Anal. Biochem., 118:197(1981)); an acidic silver staining method (see: Heukeshoven, J. and Dernick, F., Electrophoresis, 6:103(1985); Gottlieb, M. and Chavco, K., Anal. Biochem., 165:33(1987); Bassam, B. J. et al., Anal. Biochem., 98:231(1979)); a cupric-silver method (see: Switzer, R. C. et al., Anal. Biochem., 98:231(1979)) and the like. These silver staining methods are, however, proven to be less satisfactory in the sense that they cannot detect DNA to the level of ng and are not reliable in a view of accuracy and reproducibility.
Accordingly, there are strong reasons for exploring and developing an improved method for detecting DNA with a high sensitivity.